Emergency monitoring on Nore bridge in Moss

Nore Bridge was closed to all traffic on Thursday 15 April. It affected many people. The 57-year-old bridge on county road 120 is part of the main motorway between Moss and Våler. Large companies such as Europris are located on the eastern side of the bridge. It is also used by long-distance lorries from Moss in the direction of the E18.

The bridge was closed after a ground failure in the area where there is a lot of clay. The ground breaking may be related to the construction of a new road. It is being built to establish a new water supply between Moss and Vestby. It's an extensive NOK 135 million project that is scheduled for completion next summer.

- We don't know if this work will be delayed. The new water pipeline is nine kilometres long. We are continuing to work on other parts of the line," says Kaj-Werner Grimen, sector manager at Movar (Mosseregionen vatten og avløp).

Fast response

Twenty-four hours after the collapse, Cautus Geo was on site with instruments to document exactly what was happening in the ground.

- It was crucial that Cautus Geo could instrument the area so quickly. It ensured automatic and continuous measurement around the clock. It actually provided knowledge that ensured that the ground was completely stable so that the bridge could be reopened," says Hans Vebjørn Kristoffersen, project manager at Cowi.

It took five days before the bridge could be partially reopened. By then, up to 25 people had been at work over the weekend and in the days that followed.

Cowi is designing

Cowi has been engaged by Movar to design the work on the new water supply. The work past the Nore bridge has not yet been restarted.

- "We need to find the cause of the ground rupture. Next, the area must be geotechnically analysed," says Kristoffersen.

Movar also emphasises the importance of instrumentation in ensuring that traffic could be reopened on the bridge before a week had passed.

- "The fact that Cautus Geo was so quickly able to establish automatic monitoring that gave us actual knowledge of the ground conditions, with ongoing documentation, was a great help in the assessment to be able to reopen the bridge," says Grimen.

Continued measurement

Work on the water supply past the Nore bridge has not yet been restarted. In the meantime, traffic on the bridge is running as normal. It is very busy. The daily traffic is 9000 vehicles.

- "We will still have instrumentation in the area. Among other things, we will have inclinometers in boreholes. This will provide us with actual measurements of any displacements down in the ground," says Kristoffersen at Cowi.

Cautus Web collects and analyses data. Everything is available in a web interface. In Moss, it was set up with various analyses and alarm levels with SMS and e-mail to the project group.

- This means that all information is available to everyone in the project at all times. That's a big advantage. In addition, notification is established in the event of deviations," says Kristoffersen.

• Automatic total station for 24 prisms on bridge pillars, points in the terrain and solid rock (reference points).

• Six pore pressure gauges at three points are installed around the bridge to measure changes in pore pressure and groundwater level.
• Inclinometers will be installed in boreholes. Will measure 3D deformations in the ground when the work starts up again.
• Cautus Web collects all data from the instrumentation and provides notification (e-mail and SMS) if limit values are breached.